1. Technical Field
The present invention concerns an event simulator for telecommunication networks, in particular MS-SPRING (Multiplexed-Shared Section Protection Ring) optical fiber telecommunication networks, comprising a set of network elements, whose operation has to be tested, and events simulation means. The present invention further relates to a method for simulating the operation of such a telecommunication network.
2. Background Art
In present telecommunication networks it has become extremely significant to be able to obviate to failures occurring in said networks without jeopardizing their functionality.
Therefore, telecommunication networks, particularly optical fiber networks, are provided with protection means against possible occurring of network element failures.
For instance, a Multiplexed Shared Section Protection Ring, or MS-SPRING, network is a set of network elements arranged in a topology of optical fiber network wherein a distributed protection mechanism is implemented providing for automatic restart should any faults arise in the connection fibers. By MS-SPRING network a kind of network is meant wherein network elements are connected using data sequences according to SDH structures (Synchronous Digital Hierarchy).
MS-SPRING networks perform automatic traffic restart through a synchronized rerouting of said traffic, which is actuated at each ring node. This operation is controlled by a protocol consisting of 16-bit configured bit patterns, which are continuously transmitted/received between adjacent nodes of the network.
Said protocol is based on two bytes contained in the overhead of SDH frame, called K1 and K2. Bytes K1 and K2 contain information, which can be read and written by each ring node for traffic rerouting.
Said protocol and operations involved by it with reference to the different bit patterns are defined by many international Standards issued by ANSI, ITU-T and ETSI.
Reference should be made e.g. to xe2x80x9cCCITT Recommendation G 841, draft, April 1995xe2x80x9d.
Two MS-SPRING network types are defined by Standards, one for two-fiber rings, i.e. those in which each ring node is connected with another node by a span consisting of two optical fibers, carrying signals propagating in opposite direction, the other for four-fiber rings which is able to carry a higher traffic.
FIG. 1 shows an MS-SPRING two-fiber network ring 1. Said ring 1 consists of a set of 6 network elements or nodes NE. In general, network elements NE may be in a number of 2 to 16. Each network element NE has two bi-directional communication ports PO, with each port operating both for transmission and reception. One communication port PO is dedicated for clockwise traffic E, the other for counterclockwise traffic W.
Two adjacent network elements NE are connected one to each other by a span SP, which span consists of two connections CN, with each of them being obtained by an optical fiber and forwarding traffic in opposite directions, i.e. one in clockwise direction E, the other in counterclockwise direction W.
In MS-SPRING network ring 1 the bandwidth is divided in two halves of equal capacity, called work capacity and protection capacity. Work capacity is used for high priority traffic, whereas protection capacity is used for low priority traffic, the latter being lost in case of failure.
Protection in MS-SPRING network ring 1 is implemented according to a so-called xe2x80x9cBridge and Switchxe2x80x9d technique, which will substantially reroute traffic from its work capacity to protection capacity in opposite direction through a proper modification of network element internal connections. Switching commands for performing the Bridge and Switch are contained in the pair of bytes K1, K2 as mentioned above.
A similar protection technique, that is classified as APS (Automatic Protection Switch), requires for each network element to be equipped inside with a device called APS controller, which is able to detect line failures, communicate relevant information to the other network elements and actuate Bridge and Switch type switching.
In implementation of MS-SPRING ring networks the problem often arises having to determine in special situations the expected behavior of the network itself caused by the presence of special complex fault combinations on interconnection fibers and/or controls (manual switch, lockout, forced switch) set by network operators.
Specifically, said problem may arise in two instances:
a) when a purely theoretic analysis of an ambiguous or anyway complex scenario is preliminary desired, in order to evaluate the expected network response;
b) when there is the need of simulating in a laboratory a situation which showed malfunctions in the operating environment due to a wrong implementation of MS-SPRING functionality in the network apparatus.
A suitable solution for item (a) would be using a pure MS-SPRING network simulator, i.e. a computer with a suitable software representing a MS-SPRING virtual network model and simulating the events of interest. As regards item (b), on the contrary, the simulator should also be able to reproduce the malfunction of the network apparatus itself as a consequence of design defects.
In order to solve item (a) no dedicated solutions have been adopted so far, except adapting general software simulators for computer networks to MS-SPRING ring networks. However, this approach appears somewhat inconvenient, since such tools are designed to perform statistical analysis (i.e. many repeated tests) of packed switching protocols supporting networks, typical for computer networks. On the contrary, simulation of an MS-SPRING network will require simulation of the behavior of one situation each time and, above all, simulation of the MS-SPRING protocol, which is not provided in available simulation software libraries, since MS-SPRING protocol cannot be classified as a xe2x80x9cpacket switching protocolxe2x80x9d. Moreover, adding a new protocol to the existing ones is generally difficult and often requires some compromises due to a limited changeability of the simulation program.
To solve item (b) the only known solution is to physically reproduce the network and the event configuration which caused the problem. Such an approach is considerably expensive from a logistic and financial viewpoint, since it requires a dedicated room provided with a considerable number of apparatus (16 in the worst case) and many instruments capable of simulating degraded signal situations (optical attenuators are used to this purpose). Additionally, it is not possible to acquire and analyse information from the network elements, since it occurs in a few milliseconds without any trace left but the final state reached by said network elements. On the other hand, said final state can only be observed through the association of proper frame processors with the optical interfaces of network elements.
It is the object of the present invention to solve the above drawbacks and provide an event simulator for MS-SPRING telecommunication networks, having a more effective and improved performance.
In this scenario, it is the main object of the present invention to provide an event simulator for telecommunication networks, which does not require physical reproduction of the telecommunication network to be simulated.
A further object of the present invention is to provide an event simulator for telecommunication networks using processing means suitable for MS-SPRING telecommunication networks.
In order to achieve such objects, the present invention provides an event simulator for telecommunication networks and/or a method for simulating events for an optical fiber network incorporating the features of the annexed claims, which form an integral part of the description herein.
Further objects, features and advantages of the present invention will become apparent from the following detailed description and annexed drawings, which are provided by way of non limiting example.